Broadband antennas for receiving a broadband of radio-frequency signals are well known. Such broadband antennas generally comprise a plurality of antenna elements of different lengths electrically connected to one another such that at least one of the antenna elements is suitable for receiving and/or transmitting at a desired frequency.
It is also known to form such an array of antenna elements in a flat, generally circular configuration so as to define a broadband antenna which requires minimal volume. One example of such a circular broadband antenna is disclosed in U.S. Pat. No. 4,594,595 issued on Jun. 10, 1986 to Struckman and entitled CIRCULAR LOG-PERIODIC DIRECTION-FINDER ARRAY.
Log periodic antennas are also well known. In a log periodic antenna the elements of the antenna increase in length at a logarithmic rate and alternate such that every other element is on an opposite side of a common conductor or trunk. The benefit of such a log periodic configuration is that a substantially greater band width is achieved.
Examples of such circular log periodic antennas are provided in U.S. Pat. No. 4,063,249, issued on Dec. 13, 1997 to Bergander et al., and entitled SMALL BROADBAND ANTENNA HAVING POLARIZATION SENSITIVE REFLECTOR SYSTEM; U.S. Pat. No. 5,164,738, issued on Nov. 17, 1992 to Walter et al., and entitled WIDE BAND DUAL-POLARIZED MULTIMODE ANTENNA; and U.S. Pat. No. 5,212,494 issued on May 18, 1993 to Hoffer et al., and entitled COMPACT MULTI-POLARIZED BROADBAND ANTENNA.
It is worthy to note that various different linear polarizations, as well as the ability to receive and transmit circularly polarized signals, are achieved in Hoffer et al., and Walter et al., by forming the circular antenna assembly to comprise two orthogonal log-periodic antennas. By way of contrast, Bergander utilizes two separate orthogonal antenna assemblies to achieve the same result.
Although log-periodic antennas have proven generally suitable for their intended uses, such conventional antennas are generally too thick to be utilized in applications wherein it is desirable that the antenna be disposed as flush as possible to the surface upon which the antenna is mounted. Such flush mounting of an antenna is particularly desirable in aircraft applications, wherein it is desirable to minimize aerodynamic drag by streamlining the fuselage, wings, and any other aerodynamic surfaces thereof. It is particularly important to minimize drag in aircraft which fly at high speeds, as well as those which must fly for considerable distances without refueling. For example, the Unmanned Air Vehicle (UAV) is an unmanned military surveillance aircraft which must fly a considerable distance without refueling. Thus, it is desirable to minimize drag upon the aircraft, so as to increase the effective range thereof.
It is also desirable to provide an antenna which is conformal, i.e., which conforms generally to the curvature or shape of the surface upon which it is mounted. The use of such a conformal antenna further minimizes undesirable aerodynamic drag by tending to maintain the general shape of the surface upon which it is mounted. The use of such a conformal antenna also minimizes distortion or modification of such a surface. That is, the surface does not require modification in order to accommodate the antenna.
Thus, as those skilled in the art will appreciate, it is desirable to provide a broadband log-periodic antenna assembly which is comparatively thin and therefore does not extend substantially above the surface upon which is it mounted and which may be formed so as to be generally conformal to that surface.